Insulating film and method of producing semiconductor device

ABSTRACT

A silicon oxide film is formed to cover an island non-monocrystalline silicon region by plasma CVD using an organic silane having ethoxy groups (e.g., TEOS) and oxygen as raw materials, while hydrogen chloride or a chlorine-containing hydrocarbon (e.g., trichloroethylene) of a fluorine-containing gas is added to the plasma CVD atmosphere, preferably in an amount of from 0.01 to 1 mol % of the atmosphere so as to reduce the alkali elements from the silicon oxide film formed and to improve the reliability of the film. Prior to forming the silicon oxide film, the silicon region may be treated in a plasma atmosphere containing oxygen and hydrogen chloride or a chlorine-containing hydrocarbon. The silicon oxide film is obtained at low temperatures and this has high reliability usable as a gate-insulating film in a semiconductor device.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for producing agate-insulating film which is used in a thin film device such as agate-insulated field effect transistor or the like, at a low temperatureof 650° C. or lower, and also to the insulating film produced by themethod.

BACKGROUND OF THE INVENTION

[0002] Heretofore, in a thin film device such as a gate-insulated fieldeffect thin-film-transistor (TFT) or the like, a silicon oxide film withgood characteristics, which is obtained by forming a crystalline siliconfollowed by heating and oxidizing its surface at high temperaturesfalling within a range of from 900 to 1100° C., has been used as agate-insulating film.

[0003] The oxide film formed by such thermal oxidation is essentiallycharacterized in that its interfacial level density is extremely low andthat it may be formed on the surface of a crystalline silicon at auniform thickness. Accordingly, the former brings about good on/offcharacteristics and long-term reliability on bias/temperature; while thelatter reduces the short circuit between a gate electrode and asemiconductor area (active layer) at the edges in an islandsemiconductor region to thereby improve the production yield ofsemiconductor devices.

[0004] To use such a thermal oxide film in producing semiconductordevices, however, a material which is resistant to high temperaturesmust be selected as the material for the substrate. In this respect,since inexpensive glass materials (for example, alkali-free glass suchas Corning 7059, etc.) cannot be used, the production costs aredisadvantageously high especially when large-area substrates are used.Recently, a technical means for forming TFT on an alkali-free substrateis being developed, in which, however, a thermal oxide film cannot beused but a gate-insulating film shall be formed by sputtering or byphysical or chemical vapor deposition (CVD) such as plasma CVD orreduced pressure CVD.

[0005] However, it was inevitable that the characteristics of thesilicon oxide film formed by such means were inferior to those of thethermal oxide film. Namely, the interfacial level density of the formeris generally large and, additionally, the former was always accompaniedby the dangers of alkali ions such as sodium ions or the like invadingthe film being formed. In addition, since the step coverage of thesilicon oxide film is not so good, the film frequently caused the shortcircuit between the gate electrode and the active layer at the edges ofthe island semiconductor region. For these reasons, it was extremelydifficult to obtain semiconductor devices of the kind satisfying all thecharacteristics, the reliability and the production yield by the priorart technology.

SUMMARY OF THE INVENTION

[0006] The present invention has been made so as to solve at least oneof these problems in the prior art technology. Accordingly, one objectof the present invention is to provide a method for producing a siliconoxide film with good step coverage. Another object of the presentinvention is to provide a silicon oxide film which is resistant tounfavorable impurities such as alkali ions and others and also toprovide a method for producing the film.

[0007] First, the present invention is characterized in that a filmwhich has been obtained by plasma CVD using a mixed gas containing anorganic silane having ethoxy groups, oxygen, and hydrogen chloride or achlorine-containing hydrocarbon, as the raw material gas, and consistsessentially of silicon oxide is used as a gate-insulating film.

[0008] Secondly, the present invention is also characterized in that afilm which has been obtained by plasma CVD using a mixed gas containingan organic silane having ethoxy groups, oxygen, and afluorine-containing gas (e.g., NF₃, C₂F₆), as the raw material gas, andconsists essentially of silicon oxide is used as a gate-insulating film.

[0009] Accordingly, the present invention provides an insulating filmconsisting essentially of silicon oxide, which has been formed on anisland non-monocrystalline semiconductor region consisting essentiallyof silicon to closely cover the region and is characterized in that from1×10¹⁷ to 5×10²⁰ cm⁻³ of halogens are detected from the film bysecondary mass spectrometry and that 5×10¹⁹ cm⁻³ or less carbons aredetected therefrom.

[0010] The present invention also provides a first method of producing asemiconductor device comprising a first step for forming an islandnon-monocrystalline semiconductor region consisting essentially ofsilicon and a second step for forming a film consisting essentially ofsilicon oxide over the non-monocrystalline semiconductor region in aplasma atmosphere resulting from a mixed gas containing an organicsilane having ethoxy groups, oxygen, and hydrogen chloride or achlorine-containing hydrocarbon.

[0011] The present invention further provides a second method ofproducing a semiconductor device comprising a first step for forming anisland non-monocrystalline semiconductor region consisting essentiallyof silicon, a second step for exposing the island semiconductor regionto a plasma atmosphere containing oxygen, and hydrogen chloride or achlorine-containing hydrocarbon, and a third step for forming a filmconsisting essentially of silicon oxide over the non-monocrystallinesemiconductor region in a plasma atmosphere resulting from a mixed gascontaining an organic silane having ethoxy groups and oxygen.

BRIEF EXPLANATION OF THE DRAWINGS

[0012]FIG. 1(A) is a conceptual cross-sectional view showing a positivecolumn CVD apparatus used in an example of the present invention.

[0013]FIG. 1(B) is a conceptual plan view showing the positive columnCVD apparatus shown in FIG. 1(A).

[0014] FIGS. 2(A) to 2(E) shows a flow sheet showing the formation ofTFT in the example.

[0015]FIG. 3 shows the characteristic curves of breakdown voltage of theinsulating films obtained in the example.

[0016] FIGS. 4(A) and 4(B) show the characteristic curves of V_(FB) ofthe insulating films obtained in the example.

DETAILED DESCRIPTION OF THE INVENTION

[0017] As the organic silane having ethoxy groups, preferred aresubstances to be represented by chemical formulae. Si(OC₂H₅)₄(tetraethoxysilane, hereinafter referred to as TEOS), Si₂O(OC₂H₅)₆,Si₃O₂(OC₂H₅)₈, Si₄O₃(OC₂H₅)₁₀ and Si₅O₄(OC₂H₅)₁₂. Since these organicsilane materials move on the surface of the substrate for a long periodof time to be decomposed on the surface to form a silicon oxide filmthereon, they may well get into even hollows to give an excellent filmwith good step coverage.

[0018] As the chlorine-containing hydrocarbon, preferred are substancesto be represented by chemical formulae C₂HCl₃ (trichloroethylene),C₂H₃Cl₃ (trichloroethane) and CH₂Cl₂ (dichloromethane). Thechlorine-containing gas of the kind is decomposed essentially in a vaporphase to be compounded with alkali elements such as sodium or the likethat exists in the filming atmosphere, whereupon the resulting compoundremoves from the substrate to accelerate the removal of alkali elementsfrom the silicon oxide film being formed. Some chlorine atoms stillremain in the silicon oxide film formed, and these function as a barriertherein against alkali elements which will try to invade the film fromthe outward later on. As a result, the reliability of TFT may beimproved. The concentration of the chlorine-containing hydrocarbon ispreferably from 0.01 to 1% relative to the whole mixed gas. If it ismore than 1%, the gas will have bad influences on the characteristics ofthe film formed.

[0019] In the insulating film consisting essentially of silicon oxide,thus formed by the above-mentioned method, halogen elements (e.g.,fluorine or chlorine) are detected in an amount of from 1×10¹⁷ from5×10²⁰ cm⁻³ as impurity elements by secondary ion mass spectrometry,while the carbon concentration is 5×10¹⁹ cm⁻³ or less. In particular, inorder to lower the interfacial level density of the film, it is desiredthat the carbon concentration is 1×10¹⁸ cm⁻³ or less. In order to lowerthe carbon concentration, the temperature of the substrate duringfilming may be 200° C. or higher, preferably 300° C. or higher.

[0020] On the insulating film to be formed in this manner, many danglingbonds are often precipitated in the initial stage of its filming.Therefore, it is preferred to previously expose the substratesemiconductor layer (this preferably consists essentially of silicon) toa plasma atmosphere containing oxygen. As a result, the interfaciallevel density is lowered while the fluctuations of the flat bandpotential in the bias/temperature test are reduced, and therefore thereliability of the semiconductor device to be formed is improved. It isalso preferred to add to the atmosphere hydrogen chloride or achlorine-containing material such as trichloroethylene, trichloroethane,dichloromethane or the like, in addition to oxygen, to further improvethe effect.

[0021] On the other hand, after the formation of the insulating filmconsisting essentially of silicon oxide by the above-mentioned method,the film may further be heat-treated at temperatures falling within therange of from 200 to 650° C. to thereby reduce the fluctuations of theflat band potential. The heat treatment is preferably conducted in anoxygen-free atmosphere such as argon, nitrogen or the like. Thefluctuations of the flat band potential are noticeably reduced by theheat treatment at 450° C. or higher and the reduction is saturated at600° C. or higher.

[0022] The second method of the present invention is characterized bycomprising exposing an island non-monocrystalline semiconductor regionconsisting essentially of silicon to a plasma atmosphere containingoxygen, and hydrogen chloride or a chlorine-containing hydrocarbon,followed by forming a film consisting essentially of silicon oxide overthe non-monocrystalline semiconductor region by plasma CVD using a rawmaterial containing an organic silane having ethoxy groups and oxygen.

[0023] In the second method, hydrogen chloride or a chlorine-containinghydrocarbon is essentially accumulated in the chamber during the plasmatreatment, which brings about the same effect as that to be broughtabout by the above-mentioned first method where hydrogen chloride or achlorine-containing hydrocarbon is added, during the following step offorming the silicon oxide film. The same as that mentioned above shallapply to the second step with respect to the improvement in thereliability attainable by the plasma treatment. To obtain a betterresult from the second method, it is also preferred that the chlorineconcentration and the carbon concentration in the silicon oxide filmthus formed by the second method are the same as those in the filmformed by the above-mentioned the first method. It is also preferred inthe second method that the film consisting essentially of silicon oxidethus formed is subjected to heat treatment at 200 to 650° C., preferablyat 450 to 600° C., after the filming in order to obtain a further betterresult.

[0024] The plasma CVD apparatus to be employed in the present inventionmay be either an ordinary parallel plate-type apparatus (in which a pairof electrode plates are located in a chamber, facing to each other, andone or both of them has/have a sample substrate mounted thereon) or apositive column-type apparatus such as that used in the followingexample.

[0025] However, the latter is preferred to the former in view of thefollowing two points. One is that the amount of the substrates to betreated at one time is determined by the area of the electrodes used inthe former, while it is determined by the discharging volume in thelatter. Accordingly, a larger amount of substrates may be processed atone time by the latter. The other is that the surface of the substratetreated by the former is much damaged by the plasma, while the latter isalmost free from the damage by the plasma since it has almost nopotential inclination. In addition, since the uniformity of the film tobe formed using the latter is better than that using the former, theuniform film has no bad influences on the characteristics of TFT and theproduction yield thereof.

[0026] It is necessary that. the chamber of the plasma CVD apparatus tobe used for the filming in the present invention is sufficientlycleaned, prior to its use, so as to reduce the content of alkalielements, such as sodium, etc., in the chamber. To clean the chamber,chlorine, hydrogen chloride or the above-mentioned chlorine-containinghydrocarbon may be introduced into the chamber along with oxygen, andthereafter the plasma may be generated therein. It is preferred that thechamber is heated at 150° C. or higher, preferably 300° C. or higher, soas to more effectively carry out the step.

EXAMPLE

[0027] This example demonstrates one embodiment of the present inventionof forming a silicon oxide film, as the gate-insulating film, on anisland non-monocrystalline silicon semiconductor film by positive columnplasma CVD, essentially showing the electric characteristics of thesilicon oxide film formed. The plasma CVD apparatus used herein is shownin FIG. 1. FIG. 1(A) is a vertical cross-sectional view of theapparatus, and FIG. 1(B) is a top plan view of the same. The positivecolumn CVD is characterized in that the substrate to be coated islocated in the positive column region for plasma discharging and iscoated with films therein.

[0028] The RF power sources 102 and 103 give the power to generateplasma. Regarding the frequency from the sources, radio waves aretypically employed, having a frequency of 13.56 MHz. The power fed fromthe two power sources is adjusted by the phase shifter 104 and thematching boxes 105 and 106 in such a way that the condition of theplasma to be formed is the best. The power derived from the RF powersources arrives at the pair of electrodes 107 and 108 that have beenlocated in parallel to each other in the inside of the chamber 101 andhave been protected by the electrode covers 112 and 113, thus causingdischarging between these electrodes. Substrates to be treated arelocated between the electrodes 107 and 108. In order to improve themass-producibility, the substrates 111 are cased in a container 109,where they are attached to the both surfaces of the sample u holders110. The substrates are characterized in that they are parallel to eachother between the electrodes. The substrates are heated by the infraredlamp 114 and kept at suitable temperatures. Though not shown, theapparatus is fitted with a gas exhauster and a gas-feeding means.

[0029] The filming conditions and the characteristics of the film formedare mentioned below. The temperature of the substrates was 300° C. Intothe chamber, 300 SCCM of oxygen, 15 SCCM of TEOS and 2 SCCM oftrichloroethylene (hereinafter referred to as TCE) were introduced intothe chamber. The RF power was 75 W, and the whole pressure was 5 Pa.After the filming, the film formed was annealed in hydrogen atmosphereat 350° C. for 35 minutes.

[0030]FIG. 3 shows the results of the dielectric breakdown test of thesilicon oxide films of 1000 Å thick that had been formed onhigh-resistance silicon wafers using the present apparatus. Over thesilicon oxide film, formed was a 1 mmø-aluminum electrode and therelation between the voltage and the current was plotted. FIG. 3(C)indicates the film that had been formed on the substrate without anyparticular treatment of the substrate prior to the filming, from whichit is noted that the breakdown voltage of the film is low. The films ofFIG. 3(A) were formed as follows: After the substrates were set in thechamber, they were heated at 300° C. and exposed to the plasmaatmosphere generated by introducing 400 SCCM of oxygen and from 0 to 5SCCM of TCE. The total pressure of the atmosphere was 5 Pa, and the RFpower was 150 W. The plasma exposure was carried out for 10 minutes.(During the step, no film was formed by the gaseous reaction.) After theplasma exposure, the silicon oxide films of FIG. 3(A) were formed, andthey showed a high breakdown voltage.

[0031] The films of FIG. 3(B) were formed as follows in the same manneras in FIG. 3(A) except that the flow rate of TCE in the filming step waschanged to 4 SCCM or more, for example 5 SCCM. As shown, they had a lowbreakdown voltage. From these results, it has been found that the TCEconcentration for the filming has the optimum value.

[0032]FIG. 4(A) shows the result of the bias/temperature test, as oneexample of the reliability tests, of the insulating films formed in thisexample, indicating the relation between the fluctuations (V_(FB)) ofthe flat band voltage (V_(FB)) and the pre-treatment, if any, of thesubstrates. In the bias/temperature test, a voltage of +17 V wasimparted to the sample at 150° C. for one hour and the C-Vcharacteristic of the sample was measured at room temperature. Next, avoltage of −17 V was imparted to the same sample at 150° C. for one hourand the C-V characteristic thereof was also measured at roomtemperature. The difference in V_(FB) between the two measurements wasobtained to be V_(FB).

[0033] In FIG. 4(A), the substrate of the sample (a) was notpre-treated. V_(FB) of the sample (a) was about 5 V and was relativelylarge. However, the problem was solved by pre-treating the substrate.The substrates of the samples (b) and (c) were pre-treated under theconditions mentioned below. Sample (b) (c) Temperature of Substrate 300°C. 300° C. TCE/Oxygen 0/400 0.5/400 RF Power 150 W 150 W Time forTreatment  10 min  10 min

[0034] From FIG. 4(A), it is understood that the reliability of theinsulating film was improved much more by pre-treating the substrateusing TCE.

[0035] The same improvement may also be attained by annealing theinsulating film formed. The annealing of the film was carried out inargon of one atmospheric pressure at 300 to 570° C. for one hour. Therelation between the annealing temperature and V_(FB) is shown in FIG.4(B), from which it is noted that V_(FB) was significantly reduced whenthe film was annealed at temperatures not higher than 450° C., while itbecame gradually constant when the annealing temperature was being nearto 600° C. From the result, it was clarified that the annealing of theinsulating film formed is effective in improving the reliability of thefilm.

[0036] On the basis of the results obtained from the above-mentionedexperiments, a TFT sample was produced. The flow sheet for producing itis shown in FIG. 2. First, the silicon oxide film 202 of 2000 Å thickwas formed, as a subbing film, on the substrate (Corning 7059) 201, bypositive column plasma CVD using TEOS, oxygen and TCE as raw materials.The apparatus used herein was same as that shown in FIG. 1. The mainconditions for the filming were as follows: Temperature of Substrate:300° C. Whole Pressure:  5 Pa Mixed Gas: TOES:  12 SCCM Oxygen: 300 SCCMTCE:  2 SCCM RF Power:  75 W

[0037] Next, an amorphous silicon film of 500 nm thick was depositedthereover by plasma CVD, and this was patterned to form the islandsilicon region 203. This was allowed to stand in nitrogen atmosphere at400° C. for 30 minutes to remove hydrogen therefrom. Next, this wasannealed with a laser ray, as shown in FIG. 2(A), to crystallize thesilicon region. As the laser, used was a KrF excimer laser (having awavelength of 248 nm and a pulse width of 20 nsec). The energy densitywas from 200 to 350 mM/cm². During the irradiation of the laser rays,the substrate was kept at 300 to 500° C., for example 450° C.

[0038] Afterwards, the silicon oxide film 204 of 1000 Å thick was formedto cover the island silicon region 203, as a gate-insulating film, bypositive column plasma CVD using TEOS, oxygen and TCE as raw materials,as shown in FIG. 2(B). Prior to the filming, the substrate waspre-treated, using the same apparatus as in Example 1. The mainconditions for the pre-treatment were as follows: Temperature ofSubstrate: 300° C. Whole Pressure:  5 Pa Mixed Gas: Oxygen: 400 SCCMTCE:  0.5 SCCM RF Power: 150 W Time for Treatment:  10 minutes

[0039] After the pre-treatment, the film 204 was formed. The maincondition for the filming were mentioned below. After the filming, thefilm formed was annealed in argon atmosphere at 550° C. for one hour.Temperature of Substrate: 300° C. Whole Pressure:  5 Pa Mixed Gas: TEOS: 15 SCCM Oxygen: 300 SCCM TCE:  2 SCCM RF Power:  75 W

[0040] Next, a 2% silicon-doped aluminum film of 6000 Å thick wasdeposited over the film and this was patterned to form the gateelectrode 205. Then, impurity ions (phosphorus or boron) were introducedinto the region 203 in a self-ordered manner by plasma doping, using thegate electrode 205 as the mask, to form the impurity regions 206 and207, as shown in FIG. 2(C). The area into which the impurities had notbeen introduced became the channel-forming region 208. Since the dopingwas conducted through the gate-insulating film, it needed an acceleratedvoltage of 80 kV for phosphorus and 65 kV for boron. The dose amount wassuitable from 1×10¹⁵ to 4×10₁₅ cm⁻².

[0041] Next, the impurities were activated also by annealing with laserrays, as shown in FIG. 2(D). As the laser, used was the KrF excimerlaser (having a wavelength of 248 nm and a pulse width of 20 nsec). Theenergy density was from 200 to 350 mJ/cm². During the irradiation of thelaser rays, the substrate may be kept at 300 to 500° C. After theirradiation of the laser rays, this was annealed at 350° C. in hydrogenatmosphere having a partial pressure of from 0.1 to 1 atmosphericpressure for 35 minutes.

[0042] Next, the silicon oxide film 209 of 5000 Å thick was depositedthereover as an interlayer insulating film. The silicon oxide film 209was formed by positive column CVD, using TEOS, oxygen and TCE as rawmaterials. The apparatus used for the filming was the same as inExample 1. The main conditions for the filming were as follows:Temperature of the Substrate: 300° C. Whole Pressure:  5 Pa Mixed Gas:TEOS:  30 SCCM Oxygen: 300 SCCM

What is claimed is:
 1. A semiconductor device comprising: an insulatingfilm comprising silicon oxide on an insulating surface, wherein theinsulating film includes halogen at a concentration of 5×10²⁰ cm⁻³ orless and carbon at a concentration of 5×10¹⁹ cm⁻³ or less which aredetected by second ion mass spectroscopy.
 2. A device according to claim1, wherein the halogen is chlorine.
 3. A device according to claim 1,wherein the halogen is fluorine.
 4. A device according to claim 1,wherein the insulating film includes carbon at a concentration of 1×10¹⁸cm⁻³ or less which is detected by the second ion mass spectroscopy.
 5. Adevice according to claim 1, wherein the insulating film includeshalogen at a concentration of 1×10¹⁷ cm⁻³ or more which is detected bythe second ion mass spectroscopy.
 6. A device according to claim 1,wherein the insulating film is a gate insulating film.
 7. A deviceaccording to claim 1, wherein the insulating film is an insulating filmin a thin film transistor.
 8. A device according to claim 1, wherein theinsulating film covers an even surface over a glass substrate.
 9. Adevice according to claim 1, wherein the insulating film is formed byplasma chemical vapor deposition using an organic silane.
 10. A deviceaccording to claim 9, wherein the organic silane comprises at least amaterial selected from the group consisting of Si(OC₂H₅)₄, Si₂O(OC₂H₅)₆,Si₃O₂(OC₂H₅)₈, Si₄O₃(OC₂H₅)₁₀ and Si₅O₄(OC₂H₅)₁₂.
 11. A semiconductordevice comprising: a crystalline semiconductor island on an insulatingsurface; and an insulating film including silicon oxide to cover thecrystalline semiconductor island, wherein the insulating film includeshalogen at a concentration of 5×10²⁰ cm⁻³ or less and carbon at aconcentration of 5×10¹⁹ cm⁻³ or less.
 12. A device according to claim11, wherein the concentrations of halogen and carbon are detected bysecondary ion mass spectroscopy.
 13. A device according to claim 11,wherein the halogen is chlorine.
 14. A device according to claim 11,wherein the halogen is fluorine.
 15. A device according to claim 11,wherein the insulating film includes carbon at a concentration of 1×10¹⁸cm⁻³ or less.
 16. A device according to claim 11, wherein the insulatingfilm includes halogen at a concentration of 1×10¹⁷ cm⁻³ or more.
 17. Adevice according to claim 11, wherein the insulating film is formed byplasma chemical vapor deposition using an organic silane.
 18. A deviceaccording to claim 17, wherein the organic silane comprises at least amaterial selected from the group consisting of Si(OC₂H₅)₄, Si₂O(OC₂H₅)₆,Si₃O₂(OC₂H₅)₈, Si₄O₃(OC₂H₅)₁₀ and Si₅O₄(OC₂H₅)₁₂.
 19. A semiconductordevice including at least a thin film transistor comprising: acrystalline semiconductor island on an insulating surface; a siliconoxide film over the crystalline semiconductor island; and a conductivefilm including at least one of aluminum, titanium, and titanium nitride,said conductive film being formed on the silicon oxide film, wherein thesilicon oxide film includes halogen at a concentration of 5×10²⁰ cm⁻³ orless and carbon at a concentration of 5×10¹⁹ cm⁻³ or less.
 20. A deviceaccording to claim 19, wherein the concentrations of halogen and carbonare detected by secondary ion mass spectroscopy.
 21. A device accordingto claim 19, wherein the halogen is chlorine.
 22. A device according toclaim 19, wherein the halogen is fluorine.
 23. A device according toclaim 19, wherein the silicon oxide film includes carbon at aconcentration of 1×10¹⁸ cm⁻³ or less.
 24. A device according to claim19, wherein the silicon oxide film includes halogen at a concentrationof 1×10¹⁷ cm⁻³ or more.
 25. A device according to claim 19, wherein thesilicon oxide film is formed by plasma chemical vapor deposition usingan organic silane.
 26. A device according to claim 17, wherein theorganic silane comprises at least a material selected from the groupconsisting of Si(OC₂H₅)₄, Si₂O(OC₂H₅)₆, Si₃O₂(OC₂H₅)₈, Si₄O₃(OC₂H₅)₁₀and Si₅O₄(OC₂H₅)₁₂.
 27. A semiconductor device including at least a thinfilm transistor comprising: a crystalline semiconductor island on aninsulating surface; a gate insulating film including silicon oxide onthe crystalline semiconductor island; and a gate electrode on the gateinsulating film, wherein the gate insulating film includes halogen at aconcentration of 5×10²⁰ cm⁻³ or less and carbon at a concentration of5×10¹⁹ cm⁻³ or less.
 28. A device according to claim 27, wherein theconcentrations of halogen and carbon are detected by secondary ion massspectroscopy.
 29. A device according to claim 27, wherein the halogen ischlorine.
 30. A device according to claim 27, wherein the halogen isfluorine.
 31. A device according to claim 27, wherein the gateinsulating film includes carbon at a concentration of 1×10¹⁸ cm⁻³ orless.
 32. A device according to claim 27, wherein the gate insulatingfilm includes halogen at a concentration of 1×10¹⁷ cm⁻³ or more.
 33. Adevice according to claim 27, wherein the gate insulating film is formedby plasma chemical vapor deposition using an organic silane.
 34. Adevice according to claim 33, wherein the organic silane comprises atleast a material selected from the group consisting of Si(OC₂H₅)₄,Si₂O(OC₂H₅)₆, Si₃O₂(OC₂H₅)₈, Si₄O₃(OC₂H₅)₁₀ and Si₅O₄(OC₂H₅)₁₂.